1. Field of the Invention
The present invention refers to a device including a combustion engine with a piston mechanically freely movable in a space in a housing, where the device permits combustion of a fuel mixture to produce a pushing force to the piston, an electromagnetic energy transducer, and an external current circuit connected to the energy transducer for exchange of effect in a direction to or from the energy transducer. The invention also refers to a use of the device, and a vehicle.
2. Discussion of the Related Art
A known driving source for motor vehicles, such as private cars, buses and trucks, is combustion engines with internal intermittent combustion. Combustion engines are used also in other contexts, such as for garden machines, contractor machines etc., and for generating an electric effect (a so called diesel-driven generating set). The combustion engine normally has one or several pistons moving reciprocally in a cylinder housing. The rectilinear movement of the pistons, which is provided by the intermittent combustion, is transferred to a rotary movement of a crank shaft via a connecting rod, which is mechanically connected to the pistons and the crank shaft. The rotary movement of the crank shaft is transferred to the drive wheels of the vehicle via a transmission mechanism including a gear box and a clutch device. A continuous crank shaft rotation can be obtained with a relatively oscillation-free rotational velocity in spite of a strongly varying moment by the connecting rods and the crank shaft. However, the connecting rod and the crank shaft form an extensive arrangement of shaft lines, which can cause a mechanical resonance. Furthermore, the crank shaft is generally connected with a fly wheel, which may reduce the resonance problems and absorb the effect pulsations caused by the intermittent combustion, and the impulse which is transferred to the pistons.
The transfer of energy from the pistons to the driving wheels of the vehicle via the arrangement including the connecting rods and the crank shaft results in radial forces, large energy losses and, reduces positioning accuracy for each additional mechanical arrangement which is required. To a certain extent the energy losses can be reduced by new materials having a lower friction and a higher temperature resistance, improved control possibilities of the fuel injection etc., but can never be avoided.
Due to the connection of the piston to the crank shaft, the position of the piston in the cylinder housing, for instance at the top dead center, will be predetermined. Consequently, the possibilities to vary the compression during operation are limited.
To reduce the energy losses in the transfer of energy from the piston to the driving wheels of a vehicle, for instance, so called free-piston engines have been proposed. As disclosed herein, the term free-piston engine means an engine with a piston mechanically freely movable in a cylinder housing. Consequently, there is no mechanical element, such as a connecting rod or a crank shaft, for the transfer of energy from the piston. Rather, the kinetic energy of the piston is transformed directly to electrical energy. Such an energy transformation may be provided by a magnetic element in the piston and an electromagnetic element in the wall of the cylinder housing.
U.S. Pat. No. 5,788,003 to Spiers discloses a free-piston type combustion engine for driving a motor vehicle. The engine acts with an integrated electric generator. The piston, which has an inner electrically conducting winding, is arranged to perform a reciprocating movement in relation to a surrounding outer winding. During operation, the outer winding produces a magnetizing field, wherein electric effect is generated in the inner winding. The generated electric effect is obtained from the inner winding by a mechanical commutator. The electric effect may be used by an electric motor for driving the vehicle. The commutator is subject to wear and has a limited life time. The electric generator lacks a soft magnetic flow carrier, which means that a relatively low efficiency is obtained.
U.S. Pat. No. 5,172,784 to Varela refers to a hybrid drive system for motor vehicles. The drive system includes a free-piston-like type combustion engine with two parallel cylinders for respective pistons. Each cylinder includes an integrated linear electric generator with windings and magnetic elements provided in the pistons of the engine. The magnetic elements perform a reciprocating movement, and are provided such that parts of the elements move within and parts move outside the windings to create a high flow density. To synchronize the movement of the two pistons, the two pistons are mechanically connected to each other via a synchronizing crank shaft, such that the positions of the pistons are relatively predetermined. However, this electric generator lacks soft magnetic flow carriers.
U.S. Pat. No. 5,347,186 to Konotchick refers to a linear electric generator in which a magnet and a winding move in relation to each other. The relative movement of the winding in the magnetic field generates a current in the winding, which may be used by an external current circuit. The patent describes the basic principles for magnetic induction, which is a well known phenomenon. The patent discloses a member maintained in a neutral position for the relative movement.
Furthermore, W094/26020, discloses a linear electric machine operating according to the reluctance principle. U.S. Pat. No. 4,965,864 discloses a linear electric motor operating as a pump or compressor. U.S. Pat. No. 5,081,381 discloses an electromagnetic maneuvering member with a magnetic rod linearly displaceable by three electromagnets surrounding the rod. EP-A-622887 discloses a linear pulse motor having a core, carrying a permanent magnet linearly displaceable by electromagnets of a surrounding stator. EP-A-221228 discloses an electromagnetic maneuvering device with a linearly displaceable core carrying permanent magnets. The core is displaceable by electromagnets provided in a housing and surrounding the core. JP-A-59044962 discloses an electromagnetic stator device forming a path between magnet poles for a displaceable element.
The object of the present invention is to provide a combustion engine with a high efficiency. Furthermore, it is aimed at improved control of a combustion engine.
This object is obtained by the device including a control unit, which, during the operation of the device, is arranged to control the direction of the effect which is exchanged between the energy transducer and the external current circuit. By such a control unit, it is possible to determine the instantaneous position of the piston in the housing. By returning effect to the piston via the energy transducer, the piston may be displaced to a desired position when, for instance, a combustion is to be initiated. Depending on the actual operational state, this position may be varied between different strokes of the combustion engine. The control unit with the energy transducer functions as a connecting rod with adjustable length. Simultaneously the compression may be varied and controlled, for instance depending on the instantaneous load on the combustion engine. At powerful acceleration, the compression may be increased for a larger effect output from the combustion engine, and during normal operation, the compression may be optimized with regard to emissions. In addition, the compression may be adapted to different types of fuel.
According to an embodiment of the invention, the control unit is arranged to control the size of the effect. Thus, the control possibilities are further improved with regard to the determination of the instantaneous position of the piston. Preferably, the control unit is arranged to control the size of the effect in a continuous manner.
According to a further embodiment of the invention, the control unit is arranged to control the combustion by the control. The time for initiating the combustion may be controlled. Advantageously, the device includes at least one sensor member arranged to sense the position of the piston in the housing. The sensed position is transferred to the control unit as a control parameter.
According to a further embodiment of the invention, the control unit includes at least one computer reproducing the device. The software may be stored in the computer or be provided or updated from an internal learning process or from an external source via any data-communication system. The software provides a model of the device or system. The model is adaptable to changes in the system. In the model, the different components of the device or the system are represented by different parameters and functions.
According to a further embodiment of the invention, the control unit includes a first converter, which with a first connection point is connected to the energy transducer and with a second connection point via an electric connection is connected to a first connection point of a second converter, which with a second connection point is connected to the current circuit. The converters may be realized by power electronics based on diodes and IGBT-valves (Insulated Gate Bipolar Transistor) with small silicon areas and a small thermal capacitance. Advantageously, the first converter and the second converter may be controlled by the computer.
According to a further embodiment of the invention, an energy storing member is arranged to enable storing of at least of a part of the energy generated by the combustion. Advantageously, the energy stored by the energy storing member may be utilized for positioning the piston. The energy storing member may be realized in many different manners and for instance be formed by the vehicle, wherein the kinetic energy of the vehicle is utilized for generating electric effect in the electric drive motors of the vehicle and the electric effect may be transferred to the piston via the energy transducer. Consequently, the energy storing member may be arranged to store electric energy and to be connected to the control unit, for instance, the energy storing member may be connected to the connection via a converter. The energy storing member may also include a capacitor, an electrochemical accumulator and/or a flywheel. Furthermore, the energy storing member may be connected to said space and include a pressure vessel and/or a spring member, such as a gas spring.
According to a further embodiment of the invention, the electromagnetic energy transducer includes a primary transducer member connected to the piston, and a second transducer member, which is stationary in relation to the housing. The primary transducer member is movable relative to the housing and the secondary transducer member. The movement of the piston in the housing is directly converted to electric effect without any power transfer via mechanical components. Thereby, one of the transducer members may include an electromagnetic element and another of the transducer members a magnetic element. Advantageously, the electromagnetic element includes at least one winding having connections to the external current circuit.
According to a further embodiment of the invention, the secondary transducer member includes a plurality of electromagnetic elements provided beside each other in a wall of the housing along the moving direction of the piston. At least a part of the electromagnetic elements has a different design. The differing design may refer to, for instance, the size of the electromagnetic elements, the winding density, the number of winding rounds, current loading etc.
According to a further embodiment of the invention, the electromagnetic element includes a first soft magnetic flow carrier and the magnetic element includes a second soft magnetic flow carrier. The first soft magnetic flow carrier and the second soft magnetic flow carrier may form a soft magnetic circuit.
According to a further embodiment of the invention, the magnetic element includes at least one permanent magnet producing a magnetizing field. The first soft magnetic flow carrier is provided in connection to the permanent magnet to collect and concentrate the magnetic flow from the permanent magnet so that a concentrated magnetic flow flows around the winding through the soft magnetic circuit.
According to another embodiment of the invention, the second soft magnetic flow carrier has a reluctance perpendicular to the moving direction of the piston, which varies along the moving direction of the piston. The energy transducer forms a so called reluctance machine.
According to an advantageous application of the invention, the device may be utilized for generating electric energy.
According to another advantageous application, the invention refers to a vehicle including at least one electric motor for the propulsion of the vehicle and at least a device generating electric effect to the electric motor. Such a vehicle may include connections for the output of electric effect for external consumption.